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For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2008 🢒 Impala 🢒 Diagnostic Navigation 🢒 Vehicle Diagnostic Information 🢒 Scan Tool Does Not Communicate with Low Speed GMLAN Device

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

Low Speed GMLAN Serial Data

1

2*

1

--

Ground (DLC, Terminal 5)

--

1*

--

--

* An open between the data link connector (DLC) and JX 205, or DLC pin 5 ground will only effect the communication with the scan tool. Refer to Diagnostic Aids.

1. No communication on any low speed GMLAN module

2. No communication on a specific low speed GMLAN module

Circuit/System Description

Modules connected to the low speed GMLAN serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules when the ignition switch is in any position other than OFF. The low speed GMLAN serial data circuit must be operational for the vehicle to start so the vehicle theft deterrent (VTD) module and body control module (BCM) can communicate. The low speed GMLAN serial data circuit uses JX 205 as the common connection between the modules and the data link connector (DLC).

Diagnostic Aids
    • Use the Data Link References to identify the low speed GMLAN serial data modules.
    •  This test is used for a total low speed GMLAN communication failure. If only 1 module is not communicating and sets no DTC, ensure that the vehicle is equipped with the module, then use DTC U0100-U0299 for diagnostics.
    • An open in the low speed GMLAN serial data circuit between the splice pack and a module will only effect the specific module. This type of failure will set a loss of communication DTC for the module effected, and the other modules will still communicate.
    • An open in the DLC ground circuit terminal 5 will allow the scan tool to operate to set up the vehicle on the tool and then not communicate with the vehicle. When the scan tool is to the point of communicating with the vehicle, a message on the scan tool will indicate "no CANdi module detected" and will not communicate. The vehicle modules will still communicate, and the vehicle will start.
    • An open between the DLC and JX 205 will only effect the communication with the scan tool. The vehicle modules will still communicate, and the vehicle will start.
    • The engine will not start when there is a total malfunction of the low speed GMLAN serial data circuit.
        The following conditions may cause a total loss of low speed GMLAN data communication:
       - The low speed GMLAN serial data circuit shorted to ground or voltage.
       - A module internal malfunction that causes a short to voltage or ground on the low speed GMLAN circuit.

Reference Information

Schematic Reference

    •  Data Communication Schematics
    •  Control Module References

Connector End View Reference

    •  Component Connector End Views
    •  Splice Pack Connector End Views

Description and Operation

Data Link Communications Description and Operation

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Testing

Low Speed GMLAN Initial Test

  1. Test for less than 1 ohm between the DLC ground circuit terminal 5 and ground.
    2. ⇒If greater than the specified range, test the ground circuit for open/high resistance.
  2. Ignition OFF, disconnect the harness connector (splice pack comb) at JX 205. Test for infinite resistance between the following JX 205 serial data circuit terminals and ground.
    3. • Terminal A
    • Terminal B
    ⇒If less than the specified value, test the serial data circuit for a short to ground.
  3. Test for less than 0.1 volt between the following JX 205 serial data circuit terminals and ground.
    4. • Terminal A
    • Terminal B
    ⇒If greater than the specified range, test the serial data circuit for a short to voltage.
  4. Test for less than 1 ohm on the serial data circuit between terminal A of JX 205 and terminal 1 of the DLC.
    5. ⇒If greater than the specified range, test the serial data circuit for open/high resistance.
  5. Ignition OFF, install a 3A fused jumper wire between terminal A and terminal F of JX 205. Attempt to communicate with the inflatable restraint sensing and diagnostic module (SDM). Communication should be available.
    6. ⇒If no communication is established, refer to SDM Serial Data Circuit Test.

    Important: After each connection, cycle the ignition key off for 5 seconds, then ON before attempting to establish communication.

  6. Ignition OFF, with the jumper wire still attached to terminal A, individually move the other end of the jumper wire to each of the terminals listed below and attempt to communicate with the applicable module. Communications should be available with each module listed.
    7. • Terminal D, radio
    • Terminal G, instrument panel cluster (IPC)
    • Terminal H, remote control door lock receiver (RCDLR)
    • Terminal K, TDM
    • Terminal L, HVAC control module
    • Terminal M, BCM
    ⇒If any module does not communicate, test the serial data circuit between the applicable module harness connector and the JX 205 harness connector for a short to ground or a short to voltage. If the circuit tests normal, replace the applicable module.

SDM Serial Data Circuit Test

    Important: Ensure a 3A fused jumper wire is installed between terminal A and terminal F of JX 205.

  1. Ignition OFF, disconnect the harness connector of the inflatable restraint passenger presence system (PPS) module. Attempt to communicate with the SDM. Communication should not be available.
    2. ⇒If communication is established, replace the PPS module.
  2. Ignition OFF, disconnect harness connector X3 at the heated seat control module if equipped (KA1). Attempt to communicate with the SDM. Communication should not be available.
    3. ⇒If communication is established, replace the heated seat control module.
  3. Ignition OFF, disconnect harness connector X1 at the vehicle communication interface module (VCIM) if equipped (UE1). Attempt to communicate with the SDM. Communication should not be available.
    4. ⇒If communication is established, replace the VCIM.
  4. Ignition OFF, disconnect the harness connector at the Digital radio receiver (DRR) if equipped (U2K). Attempt to communicate with the SDM. Communication should not be available.
    5. ⇒If communication is established, replace the DRR.
  5. Ignition OFF, disconnect the harness connector at the SDM. Test for infinite resistance between the following SDM serial data circuit terminals and ground.
    6. • Terminal 2
    • Terminal 3
    ⇒If less than the specified value, test the serial data circuit for a short to ground.
  6. Ignition ON, test for less than 0.1 volt between the following SDM serial data circuit terminals and ground.
    7. • Terminal 2
    • Terminal 3
    ⇒If greater than the specified range, test the serial data circuit for a short to voltage.
  7. If the circuits test normal, replace the SDM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

    •  GMLAN Wiring Repairs
    •  Control Module References for module replacement, setup, and programming